Ctenacanthiformes is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

cartilaginous fish Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

. They possessed ornamented fin spines at the front of their dorsal fins and

cladodont This is a typical Cladodont tooth, of a Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a common category of early Devoni ...

-type dentition, that is typically of a grasping morphology, though some taxa developed cutting and gouging tooth morphologies. Some ctenacanths are thought to have reached sizes comparable to the

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...

, with body lengths of up to and weights of , while others reached lengths of only . The earliest ctenacanths appeared during the

Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during ...

stage of the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

(~383-372 million years ago), with the group reaching their greatest diversity during the Early

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

(

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago * Mississippian cultures, a network of precontact cultures across the midwest and Easte ...

), and continued to exist into at least the Middle

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

(

Guadalupian The Guadalupian is the second and middle Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico an ...

). Some authors have suggested members of the family Ctenacanthidae may have survived into the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

based on teeth found in deep water deposits of

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

age in France and Austria, however, other authors contend that the similarity of these teeth to Paleozoic ctenacanths is only superficial, and they likely belong to neoselachians instead.

Taxonomy

Ctenacanthiformes are suggested to be more closely related to living

elasmobranchs Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by ha ...

(modern sharks and rays) than to

Holocephali Holocephali (Sometimes spelled Holocephala; Romanization of Greek, Greek for "complete head" in reference to the fusion of Palatoquadrate, upper jaw with the rest of the skull) is a Subclass (biology), subclass of Chondrichthyes, cartilaginous fi ...

(which includes living

chimaeras Chimaeras are Chondrichthyes, cartilaginous fish in the order (biology), order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to B ...

), though less closely than euselachians like

hybodonts Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like cartilaginous fish (chondrichthyans) which existed from the late Devonian to the Late Cretaceous. Hybodonts share a close common ancestry with modern sharks and Batoide ...

. The

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

of the Ctenacanthiformes has been questioned, with some studies recovering the group as a whole as

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

with respect to other groups of

total group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

elasmobranchs like Xenacanthiformes. Following Hodnett et al. 2024 Ctenacanthidae Dean 1909 * ''

Ctenacanthus ''Ctenacanthus'' (from , 'comb' and , 'spine') is an extinct genus of ctenacanthiform chondrichthyan. Remains have been found in the Bloyd Formation (Carboniferous Period) of Arkansas and the Cleveland Shale (Devonian Period) of Ohio in the U ...

'' Agassiz, 1837 (Late Devonian) * ''

Cladodoides ''Cladodoides'' is a genus of extinct cartilaginous fish. It appeared in the Frasnian age of the late Devonian and possibly existed in the Tournaisian age of the early Carboniferous. It has a well-described braincase and brain cavity, and has ...

'' Maisey, 2001 (Late Devonian-Early Carboniferous) * ''

Cladodus ''Cladodus'' is an extinct genus of cartilaginous fishes in the family Ctenacanthidae. As the name implies, they are a type of cladodont, primitive sharks with teeth designed to snag fish and swallow them whole, instead of sawing off chunks to s ...

'' Agassiz, 1843 (Early Carboniferous) * ''

Goodrichthys ''Goodrichthys'' is a Carboniferous genus of ctenacanthiform Ctenacanthiformes is an Extinction, extinct Order (biology), order of cartilaginous fish. They possessed ornamented fin spines at the front of their dorsal fins and cladodont-type de ...

'' Moy-Thomas, 1951 (Early Carboniferous) * ''

Troglocladodus ''Troglocladodus'' (meaning 'cave '' Cladodus or 'cave branching-tooth') is an extinct genus of cartilaginous fish in the family Ctenacanthidae. Remains are known from Mammoth Cave, Kentucky, in limestone Limestone is a type of carbonate r ...

'' Hodnett et al. 2024 (Early Carboniferous) Heslerodidae Maisey 2010 * '' Avonacanthus'' Maisey 2010 (Early Carboniferous) * '' Bythiacanthus'' St. John and Worthen 1875 (Early Carboniferous) * ''

Dracopristis ''Dracopristis'' (meaning 'dragon shark') is an extinct genus of Ctenacanthiformes, ctenacanth (a group of shark-like Chondrichthyes, cartilaginous fish) that lived during the Carboniferous Geologic time scale, period in North America, around K ...

'' Hodnett et al. 2021 (Late Carboniferous) * '' Glencartius'' Ginter and Skompski 2019 (Early Carboniferous) * '' Glikmanius'' Ginter et al. 2005 (Early Carboniferous-Middle Permian) * '' Heslerodus'' Ginter 2002 (Late Carboniferous-Middle Permian) * '' Heslerodoides'' Ivanov 2022 (Late Carboniferous) * '' Kaibabvenator'' Hodnett et al. 2012 (Early-Middle Permian) * '' Nanoskalme'' Hodnett et al. 2012 (Early-Middle Permian) "''Saivodus'' group" * '' Tamiobatis'' Eastman, 1897 (Late Devonian-Early Carboniferous) * '' Saivodus'' Duffin & Ginter, 2006 (Early Carboniferous-Middle Permian, one of the largest ctenacanths, estimated to reach in length) * '' Neosaivodus'' Hodnett et al. 2012 (Middle Permian)

References

Prehistoric cartilaginous fish orders {{Paleo-cartilaginous-fish-stub